The present invention relates to aircraft, and more particularly to the directional stability and control of aircraft.
The invention has been developed primarily for use in relation to commercial passenger aircraft, and will be described hereinafter with reference to this application. It will be appreciated, however, that the invention is not limited to this particular field of use, being also applicable to a wide variety of other aircraft including military, as well as smaller recreational aircraft.
With the increasing importance of air travel as a mode of global transportation, and in an increasingly competitive global market, there is a growing need to optimise the performance potential of commercial aircraft in a number of areas including manoeuvrability, speed, load carrying capacity, fuel efficiency, and comfort. The same factors in general terms are equally relevant to military and recreational craft.
Most conventional aircraft include wings and a tail assembly which act in conjunction with the elongate fuselage to provide lift, directional stability and control. More specifically, the wings of an aircraft typically include ailerons to control rotation about the roll axis and flaps to control lift as well as pitch. The tail assembly typically includes a horizontally oriented stabiliser or tail plane with elevators to control rotation about the pitch axis and a vertically oriented fin supporting a movable rudder to control rotation about the yaw axis. The structure and operation of these lift and control surfaces are well known to those skilled in the art, and so will not be described in further detail.
One significant limitation inherent in these conventional aerodynamic structures is that acceleration beyond certain critical limits, for example during sharp turning manoeuvres, can cause one or more of the lift or control surfaces to stall. This can also occur during relatively low speed manoeuvres, particularly take-offs and landings, where in order to generate sufficient lift, the control surfaces are presented to the incident air stream at a relatively steep angle of attack. When a stall condition is induced, the air flow around the stalled lift or control surface, which is normally smooth and streamlined, delaminates and breaks into unstable turbulence. This in turn causes the efficiency of the aerofoil surface to be dramatically reduced. This results in a loss of manoeuvrability, increased power requirements to maintain momentum, and increased fuel consumption. In some cases, the minimum degree of lift and control necessary for stable flight cannot be maintained during a stall. This has potentially catastrophic consequences.
Another disadvantage with conventional control surfaces is that they are not able to respond sufficiently quickly to changes in air density, pressure, currents and the like to counteract the turbulent effect on the aircraft as it moves rapidly through these changing atmospheric conditions. The result is buffeting and discomfort for the passengers and crew within the craft. While the problem can be overcome to some extent using computer controlled automatic pilots with rapid response times, the effect is not eliminated entirely.
A further disadvantage with conventional lift and control surfaces is that because of the propensity to stall, the general lack of responsiveness, and the practical limit to structural strength, modern aircraft lack manoeuvrability, particularly at relatively high speed.
It is an object of the present invention to overcome or ameliorate one or more of the disadvantages of the prior art, or at least to provide a useful alternative.
A control system for an aircraft, said control system including:
an aerofoil surface;
mounting means connecting the aerofoil surface to the aircraft for rotation about an axis generally normal to a longitudinal axis of the aircraft such that the effective centre of pressure of the aerofoil surface is spaced rearwardly from its axis of rotation; and
bias means operable to urge the aerofoil surface toward a central rest position while permitting limited rotational movement of the control surface away from the central rest position in response to unbalanced pressure loadings whereby unbalanced aerodynamic pressures acting on the aerofoil surface tend automatically to effect a corresponding rotation against a restoring force provided by the bias means
By virtue of this arrangement, unbalanced aerodynamic pressures acting on the aerofoil tend automatically to effect a corresponding rotation against a restoring force provided by the bias means. It is believed that this increases manoeuvrability and delays the onset of a stall condition which would otherwise result in a dramatic reduction in the efficiency and effectiveness of the aerofoil.
The aerofoil according to one aspect of the invention preferably takes the form of a control surface. The control surface may be oriented vertically, horizontally or at any intermediate angle, and as such may be configured to operate during manoeuvres involving roll, pitch or yaw.
In one preferred embodiment, the control surface includes a rudder optionally supported by a fin. In another embodiment, the control surface includes a stabiliser or tail plane, optionally fitted with elevators. A combination of both configurations is also contemplated.
In one essential embodiment, conventional control surfaces adapted to initiate directional changes are provided in the form of canard lift surfaces or wings and canard rudders, disposed toward the front of the aircraft, while control surfaces according to the present invention are integrated into the tail assembly toward the rear of the aircraft, to complement the aerodynamic response of the forward directional control surfaces.
In another essential form, the invention is embodied to include the primary lifting aerofoil of the aircraft wherein the aerofoil surface forms the separate primary wings.
Here, the lateral control aerofoils according to the invention are preferably formed integrally with the primary lift aerofoils or wings of the aircraft, and as such may be disposed substantially further forward on the fuselage from the tail assembly.